W20-2 Detour Ahead
Warns drivers that a detour is ahead and that the normal route will be interrupted, prompting them to prepare to follow an alternate path.
- Sign Name
- Detour Ahead
- General Meaning
- Warns drivers that a detour is ahead and that the normal route will be interrupted, prompting them to prepare to follow an alternate path.
- MUTCD Code
- W20-2
- Official designation
- Detour (with distance) — FHWA SHS 2024, App. B5-22
- Typical Use
- Advance warning area, ahead of the work.
- Sign Category
- Warning Signs
Specifications
- Standard Shape
- Diamond
- Background Color
- Orange
- Legend / Symbol
- Black legend
- Border
- Black
- Reflectivity
- High Intensity (for nighttime visibility)
- Compliance
- MUTCD / CA MUTCD
Standard Sizes (inches)
- 30 in Diamond30" × 30"
- 36 in Diamond36" × 36"
- 48 in Diamond48" × 48"
- 60 in Diamond60" × 60"
Material / Application Notes
Advance warning ahead of a full road closure with a signed detour. Confirm placement and supplemental plaques against the applicable CA MUTCD standard.
View this sign on the Federal MUTCD (FHWA)California Notes
California-specific application notes and adoptions may differ. Review California requirements where applicable.
What It Means / When This Sign Is Used
In the field, W20-2 Detour Ahead is typically positioned at the advance warning area, ahead of the work. Common deployments include advance warning ahead of a full road closure with a signed detour; used with M4-8/M4-9 detour markers and directional arrows; common on local street closures requiring a marked alternate route. Always confirm its size, retroreflective sheeting, spacing, and placement against the CA MUTCD 2026 and the reviewing agency before finalizing the traffic control plan.
Learn more about Detour Ahead sign requirementsWhen & Where It's Used
- Advance warning ahead of a full road closure with a signed detour
- Used with M4-8/M4-9 detour markers and directional arrows
- Common on local street closures requiring a marked alternate route
Placement on a Traffic Control Plan
- Where it sits
- Advance warning area, ahead of the work.
- CA MUTCD reference
- CA MUTCD Part 6 (Temporary Traffic Control), Chapter 6F; warning-sign design in Part 2C
- Typical minimum size
- 48" × 48" on conventional roads; 60" × 60" on expressways and freeways
California / Field Use Notes
Used in advance of a detour in a California TTC zone, ahead of the DETOUR route markers that guide traffic along the approved alternate route.
In Los Angeles, this sign must conform to CA MUTCD 2026. Work in City of LA right-of-way is reviewed by StreetsLA and the Bureau of Engineering (BOE); state highways in LA County are permitted and reviewed by Caltrans District 7; county roads are permitted by LA County DPW. Sizes, retroreflectivity, and placement must meet CA MUTCD minimums — local agencies may require larger signs based on roadway class, speed, pedestrian volume, and proximity to schools or transit.
Common Plan Review Comments
- Sign not shown at the correct advance distance for the posted speed.
- Advance warning sign missing or out of sequence on the TCP.
- Wrong size specified for the roadway classification (conventional vs. expressway).
- Sign sheeting / retroreflectivity class not noted on the plan.
Verify the detour is fully signed from the advance warning through every decision point and back to the original route. Public Ready checks detour continuity on the TCP.
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Educational reference only. This is not an official Caltrans, FHWA, or local agency publication and is not legal or engineering advice. Always verify sign selection, size, placement, spacing, and application against the current CA MUTCD 2026, Caltrans sign specifications, Standard Plans, project documents, and the reviewing agency’s requirements. Local jurisdictions may impose additional requirements, and final selection, placement, and dimensions may require engineering judgment or agency approval. Written against California MUTCD 2026 (effective January 18, 2026) and the Federal MUTCD 11th Edition. Official sources last verified June 2026.
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